Method of thermal insulation



May 15, 956 A. c. JANOS 2,745,173

METHOD OF THERMAL Q INSULATION Filed Aug. 8, 1952 2 Sheets-Sheet l Alfred G. Janos,

His Attornea.

May 15, 1956 A. G. JANOS METHOD OF THERMAL INSULATION 2 Sheets-Sheet 2 Filed Aug. 8, 1952 Inventor AHred G Janos,

His Attorney- United States Patent METHOD 0F THERMAL INSULATION Alfred G. Janos, Erie, Pa., assignor to General Electric Company, a corporation of New ork Application August 8, 1952, Serial No. 393,324

2 Claims. (Cl. 29-455) My invention relates to thermal insulation and to methods of manufacture thereof.

The present application is a continuation in part of my copending application Serial No. 236,971, filed July 16, 1951, now abandoned, and assigned to the assignee of the present application.

The present invention is an improvement over the invention of the copending application of Herbert M. Strong and Francis P. Bundy, Serial No. 236,788, filed July 14, 1951, and assigned to the same assignee as the present invention, which invention was made by said Herbert M. Strong and Francis P. Bundy prior to the present invention; Therefore, it is not intended to claim herein anything shown or described in said Strong and Bundy application, which is to be regarded as prior art with respect to the present application.

Batts of thermal insulation may comprise a plurality of glass filaments. Such batts, as presently employed, are usually of substantial thickness and resiliency. It is desirable for some purposes to compress such batts to a much smaller thickness and greater density. For example, as set forth in the above-mentioned copending application of Herbert M. Strong and Francis P. Bundy, Serial No. 236,788, filed July 14, 1951, vacuum insulation, that is insulation employing an evacuated space, may be made using a filler material comprising a plurality of glass filaments arranged in particular manner. Since the filler material must support the spaced Walls against atmospheric pressure, it necessarily is compressed substantially in use compared to its condition when not so subjected to a differential pressure of this amount. If a batt of such filler material in its uncompressed state is as sembled between the walls and then the walls are pushed together compressing the batt, glass filaments may find their way between the edges of the walls to be sealed, impairing the weld and preventing the securing or maintenance of a satisfactory low pressure between the walls. By my invention, the insulating filler material is compressed before assembly and is caused to retain its compressed form. Since the filler material is precompressed and preformed approximately to the thickness it retains during use in vacuum insulated structures, it may then be assembled between the walls with a greatly reduced amount of movement of the walls toward each other to their sealing position. Moreover even aside from the effect of compression of the batt, by my invention the likelihood of loose filaments extending beyond the side walls of the batt is reduced. Accordingly, the possibility of glass filaments finding their way between the walls in a sealing area with the resultant possibility of imperfect welds is minimized. There may be combined with this process of preforming the batt of filler material an arrangement for shaping the surfaces of the batt to provide passages for facilitating evacuation of the sealed envelope surrounding the batt.

It is an object of my invention to provide an improved thermal insulated structure.

It is another object of my invention to provide an improved method of making a filler material for use with insulated structures.

It is a further object of my invention to provide an improved method of making a filler material, particularly suitable for insulated structures employing an evacuated space.

It is still another object of my invention to provide an improved method of making a filler material which facilitates evacuation of the envelope surrounding the filler material.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention, a filler material is subjected to particular conditions of pressure and temperature to precompress and preform the material approximately to thickness necessary for the use contemplated. Additionally a material may be preformed to provide passages for facilitating evacuation.

For a better understanding of my invention, reference may be had to the accompanying drawings in which:

Fig. 1 shows a sectional view of a form of insulating structure employing a filler material treated in accordance with my invention;

Fig. 2 illustrates an insulating panel, similar to that shown in Fig. 1, in an intermediate stage of manufacture where the precompressed and preformed filler material of my invention is not employed;

Fig. 3 illustrates diagrammatically an arrangement for making the filler material in accordance with my invention;

Fig. 4 illustrates diagrammatically another arrangement for making the filler material in accordance with my invention;

Fig. 5 shows a sectional view of a form of insulating structures embodying a modified form of my invention; and,

Fig. 6 illustrates diagrammatically an arrangement for forming the filler material employed in the insulating structure of Fig. 5.

In making vacuum insulated structures or panels of the type illustrated in Fig. 1, one wall 1 of a material of relatively high heat conductivity, such as low carbon steel, may be employed. A second wall 2 of a material of relatively low heat conductivity, for example stainless steel, or alternatively of relatively thin low carbon steel is employed. This second wall 2 includes a flat central portion 2a and a rim 26 extending toward the wall 1, thereby providing a pan-shaped wall of predetermined depth. The space between the walls 1 and 2 is filled with a filler material 3 which comprises a plurality of elongated glass filaments lying in a plurality of parallel planes and randomly oriented in these planes in accordance with the invention described and claimed in the aforementioned copending application of Herbert M. Strong and Francis P. Bundy. While for simplicity of description the filaments are referred to in this specification as glass, this term is intended to embrace all filamentous materials having similar characteristics with respect to hardness, low thermal conductivity, etc. For example, quartz, rock wool slag and such materials may be employed. The walls 1 and 2 are sealed at the edges 4 in any suitable manner, as by welding, and the space between the walls is evacuated to a relatively low pressure. It will be appreciated that in order to secure a low pressure, for example below a pressure of the order of microns of mercury, and to maintain this low pressure over a prolonged period of time, it is essential that a perfect weld be secured at the sealing edges 4 of the plates 1 and 2.

The securing of this perfect weld at the sealing edges endinglbey n :thesidewaus otthebiatethese loose;ends

extending into the region 6. In addition to this characteristic,-.;of-the1filler; material, thereis no definite-obstacle to; its,lateral-;movement in; the region 6.. Hence there may; be some bowingtot the sides T,ofithe batt of fillermaterial into the region 6; moreover, the COIIIPI'CSSlHgQQf I'thE filler.- material; s s mef he r l v yo er ments,at theedgesto be twisted and displaced intorthe icnrfit. As-a-.-.resu1 om filamenf r indicated;at tend;t-;m overinto the region between, the sealing edges {4. Since the fillenmaterialgin usemust-support the-walls 1 n iz; g instadift rc fialrr ssure of app ximat ly one tmosphere-res lt ng; rom the ext rn l; atmospheric pres sure, it will be appreciated-that asubstantial. reduction in way phexample, abatt of=-filamentous glass filler mat er-ialapproximately 4'. inthickness; may be compressed to about. /2,? in thickness in the-state jshownin Fig; 1; that is, theinitial:thicknes,ofthefillermaterial greatly exceedsthe depthofl-the wall 2,. which corresponds to the final thieknesspf. the compressed filler; material. Hence: the sealing edges 4 of the plates 1 and 2 Wouldbespaced approximately; 3/zf before the force is :applied, to. the plate 2;, \lllith the, large number of glass filaments involved,;

and,with,the,. necessity.of forcing the -batt of filler materialdownwardly approximately 3 /z into thespace-within the wall l ibis-apparent that there. is a great likelihood, partieularly under mass, production manufacturing conditions, that at least some of the glass filaments may find their,way.into.,the region. 6 and, therefore between the sealingmdges, 4 .as the. sealing edges are brought into engagement. The presence of such glass filaments has, a deleterious; effect ,upon the condition of, the welds secured atthepontactingedges ofthe-walls Land 2. It is, there.- fore, quite difiicult to secure a perfect weld between the walls ,1 and, 2, and, therefore, to secure asatisfactory seal which willzenabl mainteuance of thenecessary low pressure over a prolonged period of time.

.In aceordance,with my invention, thisdifiiculty is obviated by precompressingand preforming the-batt of; fillelgmaterialto, approximately the thicknesswhich it neeessarilymust assume inthe finished strnctureto prop; erly support; the -walls. ,against the differential pressure of japproximat e ly-.v one ,atmosphere- An arrangement for,

carrying out this method, particularly applicable to cases where, it; is desired to formthe batt approximately to the lateral dimensions, .of the panel in which; it. is to, be-employed, is;showndiagrammaticallyin. Fig. 3. The batt. of filler material: 3 ,iniits. uncompressed state is placed. within ;a,,contain er; 83and a flat plate, 9, having the same;

dimensions as theainterior-of the container 8, isplaced onthetopsurfaceof the filler material 3.- The glass fila-. mentsofWhichJhefiller material 3 iscomposed are ran,- domlyorientedin;aplurality of parallelplanes in accord,- ance with the invention describedandclaimedin the atore.-.

mentioned,copending ,application of Strong and. Bundyr In carrying outthe methodof my invention, thebatt. of. fillerdmaterialis. placedwithin the container: so that, these.v

planes .in which theglass filaments are oriented are parallel to the plate-9 andtothebottom ltlofthe container,

8;. With thefiller-materiaLarranged-as showninlFig.v 3, a compressive force at least of, the order of one atmos= 91 s indicatedat 1., Like theforce applied at in the arrangement ,shown,in Fig. 2, this effects a compression of the filler material 3; However, in the arrangement shown in, Fig. 3, the side walls 12 ofthecontainer S. prevent any lateral movemeneof the filaments ,of- ,thefiller material, 3

applied to, theupper surfaceof the plate 9, as,

isretained. within the confines provided. ,by. theside .walls 12. The Walls 12 are arranged to correspond to the rim 26 of the Wall 1 employed irr the insulated structure with which the compressed filler material is to be used. Accordingly, the possibility of glass filaments in the region between the sealing edges 4 of the plates 1 and 2 in the final assembly is minimized. The-pressure employed for compressing the filler material ischosen so,as1-to. reduce the thickness of. the original batt to approximately the final thickness to be employed in the'panel-structure. De: pending upon the original thickness-oftthe filler-material employed, and. the finalithickness desired, this-pressure may, of course, be substantially greater than one atmosphere. However, his necessary that ,a pressure substantially as great as one atmosphere be employed as a minimum if the batt is to be successfully compressed to a thickness approximately that required for the final structure and is not to be further compressed'below'thiszthickness during evacuation, which, further-compression might:-

result in undesired deformation of the'walls :of theipanel.

Alternatively, the. batt of uncompressed, fillerzmaterialt:

in the 1 mannerdescribed below. and has been removed; fromjheoven and the. press, the edges thereofmay be..- trimmed, to the propersize for fitting withinany paneling which thefiller'material is to be used, so that the-possibility of loose'filaments extending beyond thewalls of.

the battand into the weld area, is minimized. This method, inwhich onlytwo flat plates are employed. and

the enclosingrcontainer, is omitted, is particularly, ap

plicable-in-situations where arelatively large batt of filler material, sufficient to provide filler material for several.

pane stis employed. After. the large batt has been treated. by- .thel,aforementioned method, it may then be cut into.

a number of pieces of the size necessary foreach of'the panels In order to retain the batt of filler material in thecompressed state and to minimize'its re-expansion, ecausc:

of,the.resilience of the filaments, to a thicker condition aiter the,pressure,exerted on the plate 9 is removed, the

bait, of filler material in its compressed state is subjected to.,atemperature-above the strain point but below'the.

point at'which, any. significant flow of the glassoccurs: Preferably theternperature is chosen in the range between the strain point 'andthe annealing point of the particular glass. or other material employed, but temperatures slightly abovethe'annealing point maybe employed, so

long as temperatures high enoughto result in significant flow of the glass areavoided. By way'of example, in the casecf borosilicate glass, such as that sold under the trade name Fiberglas and identified as Type TWF, the. strain point is 450 C. and the annealing point is 500 C.

Subjecting the filler material to a temperature above the: strain point slowlyrelieves the strains therein," and allows.

the filaments to become set in the compressedcondition,

As indicated above, preferably the maximum temperature in, treating this glass. does not exceed, 500. C; but-,ifiL' is desired to speed the operation, a somewhat higher temp taturccanube employed so long as the temperatureis not sufficiently high to result in significant flow of the; glass.. It will berealized that any substantial.increaseinthe temperature above the annealing point toward the. softeningpoint, materially increases the tendency'ior flow of glass to occur and hencefor some increase. in the, amount of contact area. between adjacent filaments to. result. Such increase in contact area, of course, increases the solidconductionof the filler material. The heating of the filler material in the manner describedabovemay.

be accomplished by placing the material withinarsuitable' When this method is employed, theres S oven while the application of the compressive force thereto is continued.

It will be realized that the time required for treating the filler material will vary widely depending on the temperature employed. This time also depends on the thickness of the batt of filler material being treated. The thicker the material, the longer is the time required for the heat to penetrate to the center thereof and to remove strains from the filaments in that region. In any event, the time of heat treatment should be sufficiently long that, with the temperatures employed, all of the filaments in the filler material are raised at least to the strain point. If suificient time is available for treating the material, temperatures just above the strain point may be preferable since this offers the greatest assurance of minimizing softening of the glass and of minimizing increase in the contact area.

After the filler material has been subjected to the aforementioned temperature for the time necessary, the container 8 is removed from the oven and the filler material is allowed to cool. After the filler material has cooled to a temperature substantially below the strain point, the pressure exerted on the plate 9 is then removed and the batt of filler material is removed.

When a batt of filler material is treated in accordance with the method of this invention, there is some re-expansion of the batt of filler material after the compressive force is removed, but the thickness of the re-expanded batt of filler material is still only a small fraction of its original thickness. For example, were a batt four inches thick compressed to a thickness of, say, about Me" and treated in accordance with the method of this invention, the batt might re-expand to, say, about when the compressive force is removed. Hence, when this batt is assembled in the panel shown in Fig. l, for example, it extends only approximately /8 above the edges 4 of the lower wall 1, the depth of the wall 2 of the panel being approximately /2". During the final assembly of the panel walls, the batt must then be recompressed only about Ms" to the approximately /2 final thickness to bring the edges 4 of the walls 1 and 2 into sealing engagement instead of the approximately 3 /2" compressive movement required where it is attempted to assemble an untreated batt in the panel. The walls are then welded at the edges to provide sealed envelope for the insulated structure. The force required to recompress the batt to its precompressed thickness is very small, being in the order of /5 pound per square inch. Unlike the situation illustrated in Fig. 2 in which an untreated batt is forced into the confines of the panel structure, there is little tendency for individual glass filaments or" this treated batt to move laterally into the weld area between the edges 4 of the walls 1 and 2. This results from the fact that the filaments, in being subjected to heat while held under pressure, take a relatively permanent set in the compressed position and the deformation of the filaments and this resultant permanent set minimizes any tendency of the filaments to move laterally under the very small force exerted to recompress them to the thickness of the panel. Moreover, the compressing of the tiller material within the container 3 during heat treatment or the trimming of the edges thereof after treatment in accordance with this invention substantially eliminates any loose ends of filaments extending beyond the side walls of the batt of filler material.

In the insulating structure of the aforementioned application of Strong and Bundy, it is important from the stand-point of minimum thermal conductivity that the glass filaments be oriented in planes extending in the general direction of the walls of the panel, that is, generally parallel to these Walls in the usual insulating structure. Were uncompressed fiiler material of the type involved forced laterally into a confined space between the walls, it is unavoidable that a substantial number of the filaments, in this process, would be oriented in a direction normal to the walls, that is, in the direction of the heat fiow between the walls. By precompressing the filler material and causing the filaments to set in the compressed form .in accordance with the present invention, the tendency for filaments to be shifted from the desired orientation to a direction normal to the walls during the final assembly of the filler material within the walls is minimized.

While it has been previously suggested that batts of glass wool material be subjected to pressure and to elevated temperature for other purposes, the resultant structures would not be satisfactory for the purpose for which the applicants filler material is proposed to be employed. In one previous disclosure, for example, only a mild pressure is employed, it being particularly required that the filler material have large spaces for permitting the passage of liquid therethrough. On the other hand, to provide a satisfactory filler material for use with insulated structures employing an evacuated space, it .is necessary that a pressure of substantially one atmosphere or more be applied to the filler material, greatly compacting the material and causing it to assume a shape and thickness suflicient to support the walls against the differential pressure existing in the final insulated structure. It has also previously been suggested that batts of glass wool be subjected to elevated temperatures without the application of any pressure other than the weight of the material itself for the purpose of fusing and compacting the glass wool into a caked mass. In the method of my invention the temperature is specifically chosen to prevent such fusion, since the fusion of the filaments increases the solid conductivity and minimizes the effectiveness of the final insulating structure.

In addition to the use of the preforming process, that is the application of pressure and heat in the manner described above, for merely reducing the thickness of the batt of filler material, there may be combined with this treatment an arrangement for forming the surfaces of the filler material to facilitate evacuation. A modified form of my invention for accomplishing this additional result is illustrated in Figs. 5 and 6. Referring to Fig. 5, the insulating structure includes walls 1 and 2 as in the form previously described. The space between the walls 1 and 2 is filled with a filler material 16 which, as in the case of the filler material 3 of the form previously described, comprises a plurality of elongated glass filaments lying in a plurality of parallel planes and randomly oriented in these planes. At least one peripheral wall 17 of the filler material 16 is spaced from the corresponding peripheral portion 18 of the wall 1 to provide a passage 19 therebetween. The insulating structure is evacuated through a conduit 20 which is connected in communication with the passage 19. The conduit 20 is connected to a vacuum pump or other evacuating apparatus (not shown) for effecting evacuation of the insulating structure. The filler material 16 is formed to provide a deformation of each face thereof. In the specific form illustrated this deformation is shown as a waffie grid pattern including a plurality of projections 21 for engaging and supporting the walls 1 and 2. These supporting projections 21 provide a plurality of passages 22 therebetween. These passages 22 communicate with the passage 19. The provision of the wafiie grid pattern and hence the passages 22 facilitate evacuation of the insulating structure by providing communication of the passage 19 and the conduit 20 with a large surface of the batt of filler material 16. In the absence of such passages, it would be necessary that gases evacuated from the filler material be drawn through the entire length or width of the filler material rather than merely through a portion of the thickness thereof, which is a much smaller dimension.

In accordance with my invention this waflie grid, or other suitable pattern, is conveniently formed simultaneously with the process of precompressing the batt of filler material in the manner described above. For accomplishing thissresult two. dies or. plates. 23. and..2,4 are proyidedlfor. engagingopposite facesofthe battoflfiller. rmrterial116i The uncompressed-filler. material is placed betweemthe twodies 23andf24 and'pressure, asjndicate diagrammatically by. the.arrows 25, is exerted on the upper die. 23"to,compress,the batt of filler. material [in the manner. describedpreviously-in connection with =.the.forms of invention shown in Figs. 1 through 4. It can be seen because of.the shape ofthe surfaces of the dies 23 andf24 thebatt offiller materialis,, in addition to being coma presseddf0rrned during the exertion of the compressive force. to provide the wafile grid pattern on the surfaces thereof.

As inithe forms previously described, thebatt of'filler materiallin, ifs compressed state is subjectedftoa tempera:

ture above the strain point but below the point at which thesurfacesof'the fillenmaterial. to providepassages for.

facilitating evacuation.

While, in the form of invention shown in.Figs.. 5 and. 6, both surfaces have been illustrated 'asincludingawaflfle gridpattern, it will be apparent that,.if desired, one.

of the dies could use a fiat. surface so. that onlya single surface offthe filler material is deformed. in. themamaer. descrihed. Additionally, whilea specific .pattern,-,name1y a waffl'egrid pattern, has been employed. for purposes of-illustration, ,it will be. apparent that any other pattern. providing passages for movement of gases along oneor both surfacesof the fillermaterial between the filler ma:

terialandlthe. correspondingwall of the sealed envelope.

could be utilized.

While Ihave shown and described specificembodiments of "my invention particularlysuitable for use with vacuum insulated structures, I .do not desire my'invention to be lithitedLto the particular details shown anddescribedfandlinteniby the appendedfclaims, to cover allmodifications-within the spirit and scopeofmy inven-. (1011;.

What I.,c1aim. as new and dBSlIZBxtO: secure: by-Letters.

Patent ofthe United'S'tates is:

1.- Av method of. manufacturing an. evacuated insulating structure which comprisesproviding a:fir-st wal1 and a second.pan-shaped wall of predetermined depthincluding a. central. portionand a rim. extending, toward,-

said'firstrwall for, spacing said. first wall fromsaid central portionoiil'said second. wall, providing. a. batt of. fillermateriaLofa? thickness greatly exceeding the depthrofsaidasecondwall,v said. batt filler material consisting, of: a plurality of elongated glass filaments, applying a force atleast of the order. of one atmosphere to compress'said batt:..to a. thickness substantially equal to the depth of said-:second wall,.and, while said force is applied, heatingsaidbatt to. a temperatureabove thestrain point of the glass filaments andmbelow' the temperatureat whichany softening and flow of the glass occurs to cause saidbatt to, substantially retain itscompressedform aftertsaid force is removed, cooling, said batt to. a temperaturesubstantiallybelow said strain point before removing-,said force, assemblingsaid compressed. batt in said paneshaped -secend, wall, bringingsaid first wall-into engagementwith said. secondwall to enclose said batt, weldingsaid first Wall to said second Wall to seal said structure, andevacuatingsaid sealed'structureto a-pressu-re of the order of micronsof mercury.

2; The v method of claim 1 in which said. batt consists of borosilicate glass-filamentsand the compressed batt is heated. to atemperature of from. 450 to 500 C. for a...p eri0d.offrom five to fifteen minutes to cause said batt-to 313111.115 compressed form after the compressing;

References Cited in the file of this patent UNITED STATES PATENTS 1,186,572" Gui'bert June 13, 1916 1,888,166 Geipel Nov. 15, 1932 1;898i977 Cbmstock Feb; 21, 1933 2,023,354 Cope Dec. 3, 1935" 2,253,884 Lown Aug. 19, 1941 2,263,217 Lillie'et a1. Nov. 18, 1941 2,271,829" Powers Feb; 3, 1942 2,565,941 Barnard Aug; 28'; 1951' FOREIGN PATENTS 137,781 Austria May 25,- 1934- 475,464 Great Britain Nov. 19; 1937 

1. A METHOD OF MANUFACTURING AN EVACUATED INSULATING STRUCTURE WHICH COMPRISES PROVIDING A FIRST WALL AND A SECOND PAN-SHAPED WALL OF PREDETERMINED DEPTH INCLUDING A CENTRAL PORTION AND A RIM EXTENDING TOWARD SAID FIRST WALL FOR SPACING SAID FIRST WALL FROM SAID CENTRAL PORTION OF SAID SECOND WALL, PROVIDING A BATT OF FILLER MATERIAL OF A THICKNESS GREATLY EXCEEDING THE DEPTH OF SAID SECOND WALL, SAID BATT FILLER MATERIAL CONSISTING OF A PLURALITY OF ELONGATED GLASS FILAMENTS, APPLYING A FORCE AT LEAST OF THE ORDER OF ONE ATMOSPHERE TO COMPRESS SAID BATT TO A THICKNESS SUBSTANTIALLY EQUAL TO THE DEPTH OF SAID SECOND WALL, AND, WHILE SAID FORCE IS APPLIED, HEATING SAID BATT TO A TEMPERATURE ABOVE THE STRAIN POINT OF THE GLASS FILAMENTS AND BELOW THE TEMPERATURE AT WHICH ANY SOFTENING AND FLOW OF THE GLASS OCCURS TO CAUSE SAID BATT TO SUBSTANTIALLY RETAIN ITS COMPRESSED FORM AFTER SAID FORCE, IS REMOVED, COOLING SAID BATT TO A TEMPERATURE SUBSTANTIALLY BELOW SAID STRAIN POINT BEFORE REMOVING SAID FORCE, ASSEMBLING SAID COMPRESSED BATT IN SAID PAN-SHAPED SECOND WALL, BRINGING SAID FIRST WALL INTO ENGAGEMENT WITH SAID SECOND WALL TO ENCLOSE SAID BATT, WELDING SAID FIRST WALL TO SAID SECOND WALL TO SEAL SAID STRUCTURE, AND EVACUATING SAID SEALING STRUCTURE TO A PRESSURE OF THE ORDER OF 100 MICRONS OF MERCURY. 